The operation could happen as soon as this weekend after being postponed by President Donald Trump late last month. It would pursue people with final deportation orders, including families whose immigration cases were fast-tracked by judges in 10 major cities such as Chicago, Los Angeles, New York and Miami.
The sweep remains in flux and could begin later, according to two administration officials, who were not authorized to discuss the matter publicly and spoke on condition of anonymity. The American Civil Liberties Union pre-emptively filed a lawsuit Thursday in an attempt to protect asylum seekers.
The impending threat of the ICE raids is being greeted with fear by some and defiance by others in the Chicagoland area.
Luz Martinez's family owns the tamale stand Sonia's Tamales in Little Village. Thursday the 23-year-old said her thoughts were split between preparing food for her customers and being prepared for the impact of the ICE deportation roundups that could target her community.
"We come her for a better future for everyone and we just come to work," said Martinez, who also lives in Little Village. "We're all scared because we all have families, I have a three year old son and we're afraid we'll be separated from our loved ones."
Martinez said she came to the U.S. from Mexico when she was four years old. She said she and her parents have green cards, but they are still worried. It's not only a concern from Martinez, it's a shared concern in the community.
"We try to keep ourselves inside the house, we try to do everything that we have to do like during the week because we've been hearing everything about ICE," Martinez said.
Lightfoot is working with community organizations to make sure undocumented immigrants know their rights.
"What we are working on is doing everything we can to push back against what the Trump administration is doing," Lightfoot said.
Lightfoot said she has told ICE officials Chicago police will not be helping and will not give agents access to its databases.
"We will not allow that to happen, and we are ready, we are ready to defend each other and defend our community and we are organized," said Mony Ruiz-Velasco, who is the president of the Board of Illinois Coalition of Immigrant and Refugee Rights.
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Local immigration rights groups said they have received credible information that the Immigration and Customs Enforcement raids will in fact go down early Sunday morning.
People across the country are being briefed in churches and schools on their legal rights and how to handle encounters with ICE agents.
Following the Trump's first announcement, Chicagoans banded together, planning demonstrations to protest those raids in the Chicago area. Lightfoot said she is standing strong behind the immigrant community as the immigration leaders say they are ready to fight back, coordinating a protest at 11 a.m. on Saturday at Daley Plaza.
ICE has issued a statement that it won't comment on details of "enforcement operations," and the White House has declined comment to ABC News.
Lightfoot said she is standing strong behind the immigrant community as the immigration leaders say they are ready to fight back, coordinating a protest at 11 a.m. on Saturday at Daley Plaza.
"Please remember that you are not alone, you have all of us, a community of allies that are here to support you, please don't forget that you are not alone," said Evelyn Venegas Cuzco, who works with Illinois Coalition for Immigrant and Refugee Rights.
The operation is similar to ones conducted regularly since 2003 that often produce hundreds of arrests. It is slightly unusual to target families, as opposed to immigrants with criminal histories, but it's not unprecedented. The Obama and Trump administrations have targeted families in previous operations.
This latest effort is notable because of the politics swirling around it.
Trump announced on Twitter last month that the sweep would mark the beginning of a push to deport millions of people who are in the country illegally, a near-impossibility given the limited resources of ICE, which makes the arrests and carries out deportation orders.
Then he abruptly canceled the operation after a phone call with House Speaker Nancy Pelosi, a California Democrat, while lawmakers worked to pass a $4.6 billion border aid package . Plus, details had leaked, and authorities worried about the safety of ICE officers.
The agency said it would not discuss specifics about enforcement operations.
"As always, ICE prioritizes the arrest and removal of unlawfully present aliens who pose a threat to national security, public safety and border security," it said in a statement.
Trump started hinting anew in recent days that more removals were coming. He said last weekend they would be starting "fairly soon."
"Well, I don't call them raids," he said. "I say they came in illegally and we're bringing them out legally."
Ken Cuccinelli, the new head of Citizenship and Immigration Services, told CNN on Wednesday that the raids were "absolutely going to happen."
Pelosi said she hoped the administration would reconsider. "Families belong together," she said.
Advocates in border areas have "received word" that up to 1,000 families are expected to arrive at an immigration center in Dilley, Texas, according to attorneys representing separated families in a long-running lawsuit.
In court papers filed Thursday, the attorneys said the government has not responded to questions about the operation.
The administration has been straining to manage a border crisis, and some officials believe flashy shows of force in deporting families would deter others migrants from coming. But others have criticized any move that draws resources away from the border at a time when the Border Patrol is detaining four times the number of people it can hold. Also, a watchdog report found filthy, potentially dangerous conditions at some stations.
The ACLU lawsuit, filed in federal court in New York, argued that thousands of migrants fleeing violence in El Salvador, Guatemala and Honduras were not allowed a fair chance to request asylum due but were still ordered removed from the country. They are asking that those individuals get another hearing.
Others said they were skeptical that Trump would follow through on the threat.
Advocates have ramped up know-your-rights training since Trump took office, reminding immigrants, regardless of their immigration status, about their right to remain silent and to ask authorities for proper paperwork.
They have also explained that immigrants can often avoid arrest simply by not opening doors to agents, who need permission to enter private homes. That has forced ICE officers to wait outside courthouses and other public places to make arrests.
"We don't want to alarm folks, but we want to alert folks," said Melissa Taveras of the Florida Immigrant Coalition.
The Associated Press contributed to this report.